The present invention relates in general to a charge coupled device (CCD) for an image sensor, and more particularly to a linear color CCD suitable for sensing a color image and a method of driving the same.
Referring to FIG. 1, there is shown a construction of a conventional linear color CCD for an image sensor. As shown in this drawing, the conventional linear color CCD comprises three CCD sets corresponding to three primary colors of light, red, green and blue colors, respectively.
Each of the three CCD sets includes a photodiode (PD) array 3, 4 or 5, a pair of shift gates 2 disposed on the upper and lower surfaces of the PD array 3, 4 or 5, respectively, and a pair of horizontal CCD (HCCD) analog shift registers 1. One of the HCCD analog shift registers 1 is disposed over the upper shift gate 2 and the other is disposed under the lower shift gate 2. Each of floating diffusion (FD) elements 6 is connected to an output of a corresponding one of the CCD sets. Each of sensing amplifiers 7 is connected to an output of a corresponding one of the FD elements 6.
The operation of the conventional linear color CCD with the above-mentioned construction will hereinafter be described.
In each of the CCD sets, signal charges produced by photoelectric conversion of PDs in the PD array 3, 4 or 5 are shifted to the HCCD analog shift registers 1 when the shift gates 2 are turned on. At this time, the shifting of the signal charges from the PDs in the PD array 3, 4 or 5 through the turned-on shift gates 2 is performed in such a zigzag manner that the signal charges from the PDs of the odd number are shifted to the lower HCCD analog shift register 1 and the signal charges from the PDs of the even number are shifted to the upper HCCD analog shift register 1. The upper and lower HCCD analog shift registers 1 shift the signal charges from the PDs in the PD array 3, 4 or 5 again to the right in response to HCCD clock signals. Then, the FD element 6 and the sensing amplifier 7 cooperate to produce a signal based on the signal charges from the upper and lower HCCD analog shift registers 1.
The three linear color CCD sets corresponding respectively to the red, green and blue colors have the same construction except color filter application and, thus, the operations thereof are substantially the same. With the same construction, the three linear color CCD sets output red (R), green (G) and blue (B) color signals, respectively.
However, the above-mentioned conventional linear color CCD has a disadvantage in that the construction is more complex by three times than that of a linear black and white CCD since it requires two HCCD analog shift registers, one FD element and one sensing amplifier in the unit of one photodiode array. Also, a space is large between the adjacent photodiode arrays because two shift gates and two HCCD analog shift registers are present therebetween. This results in a degradation in a vertical color separation.